The present invention relates to a combined drilling and threading tool including an elongated shank and a conical front portion arranged in its front end and provided with two cutting edges extending symmetrically from the center of the tool and symmetrically extending ribs which are provided with cutting teeth of mutually identical profiles and which are separated by symmetrically extending chip flutes. Furthermore the invention relates to a method for drilling and threading.
In order to conduct machining operations, such as drilling and thread milling, different types of tools have been commonly used which have been optimized for each machining. The drilling operation has been conducted by means of a tool such as a drill provided with hard metal inserts or a solid drill of hard metal or speed steel. In order to be able to cut an internal screw thread after drilling it is necessary to change tool in the machine. A tool, such as a tap or a boring bar, is mounted instead of the drill. In the latter case the boring bar has been provided with a radially projecting thread cutting insert at its front end which has a cutting edge having the thread profile corresponding to the thread to be machined in the work piece.
For reducing of costs in the work shops it is most desirable to use a combination tool which provides for several different operations in succession without downtime for tool exchange in the machine.
The objects of the present invention are to provide a combined drilling and threading tool of a new type which provides for drilling and threading with large feed and cutting speeds and that simultaneously provides for a favourable chip flow.
The tool is characterized in that an inner cutting edge portion extending radially inwards to the center of the tool has a contour different from the contour of a radially outer portion of the same cutting edge and in that a sufficient clearance surface and chip flow space are provided adjacent to said inner cutting edge portion and in that teeth are formed without pitch and with mutually identical axial spacing on the ribs, said ribs provided with teeth extending towards the front portion of the tool.